Regenerative medicine in which cells are transplanted to an affected area pursuant to the objective of regenerating a lost organ is increasingly in practical use. Conventionally, an absorbent material that would provide the cells with a scaffolding inside the body was necessary to affect regeneration of large organs. Although use of animal-derived collagen and hydrolyzed artificial polymers as these absorbent materials has been tried, adequate effects have yet to be attained in terms of safety and cost. Therefore, the present inventors developed a method in which three-dimensional structures are built entirely from cells (Japanese Laid-Open Publication 2004-357694, “Tissue Plug Production Method”). In this method, by pouring a cell cluster into a mold, the creation of large structures composed only of cells, which was conventionally held to be extremely difficult, was achieved. This invention has had its efficacy confirmed in animal experiments, has progressed to the initial phase of clinical application, and is attracting attention.
According to the above-mentioned cell plug production method, by pouring cell clusters of different strains into a culture vessel, etc. in order, it is possible to create a layer-like complex cell structure. However, since organs have an even more complex sequence structure of cells, the development of a method for creating cell plugs that can assume a more arbitrary sequence structure is necessary. Further, as cell structures grow larger and more complex, supply of culture medium to the structure interior (during culturing) and blood vessel channels must be secured and further improved when performing large organ regeneration thereafter.
In recent years, special gelatin that hardens at approximately 37 degrees and turns to liquid at low temperatures has been developed (temperature-sensitive gelatin). Attempts are being made to construct three-dimensional cell structures by adhering cells to this gelatin to create cell sheets, and further stacking cell sheets upon one another. However, supplying culture medium to the interior of the cell structures is extremely difficult through the use of this method, and the thickness of structure appears to be limited to approximately 2 mm. Further, according to this method, following completion of the structure, gelatin can be recovered from the interior of the structure after the temperature has been lowered to convert the temperature-sensitive gelatin into a liquid. However, it is doubtful that gelatin can be completely recovered from inside the structures, and residual gelatin in the body presents a risk of side effects due to foreign-body reaction (Regeneration of Cartilage Tissues Using Mebiol® Gel Internet at www.mebiol.co.jp/rd-img/nankotu.pdf).